Clomazone is the common name for the herbicide 2-(2-chlorophenyl) methyl-4,4-dimethyl-3-isoxazolinone. It is a colorless to light brown and viscous liquid above room temperature, which forms a white crystalline solid when cooled. It is not flammable in nature.
Clomazone has the following chemical structure:

Clomazone is a highly effective herbicide, but unfortunately is also highly volatile. The amount of clomazone applied to the soil in a target area may move to adjacent areas and cause discoloration. This discoloration is typically in the form of whitening or some degree of bleaching, of a variety of crops, trees, or decorative plants. This bleaching, which is also indicative of the mode of action of the herbicide, may be temporary when plants are exposed to sufficiently low concentrations. However, bleaching of the crops, trees or decorative plants is undesirable even when it does not result in the destruction of the plant.
Clomazone is a broad spectrum herbicide used for control of annual grasses and broadleaf weeds in cotton, peas, pumpkins, vegetables, sweet potatoes, tobacco, winter squash and fallow wheat fields. It can be applied early preplant, preemergent or preplant-incorporated depending on the crop, geographical area and timing. Because clomazone is an inhibitor of plant pigments, users must exercise caution to avoid drift or vapors which may cause bleaching damage to non-target foliage.
Clomazone is relatively stable to degradation by UV light. It is highly volatile and can drift during or after application, causing damage to sensitive, non-target plants such as ornamental trees and shrubs, roses, small grains, alfalfa, sunflowers, and vegetable crops. Clomazone is slightly soluble in water, but it has a moderate tendency to adsorb to soil particles. It therefore has a low to moderate potential to contaminate groundwater.
Hitherto, a non-encapsulated emulsifiable concentrated formulation of clomazone has been available. However, upon application of the conventional emulsifiable concentrated formulation, the sensitive plants surrounding the intended targets of application displayed varying degrees of whitening due to the high volatility of clomazone. Thus, an encapsulated formulation of clomazone was desirable which was believed to be capable of reducing the volatility of clomazone and improve the active component delivery to the targeted plants.
Attempts to prepare formulations of encapsulated clomazone by encapsulating clomazone in polyurea and polyamide polymeric shells frequently resulted in formulations that not only gave little or no reduction in volatility, but had poor physical characteristics such as undesirable agglomeration of the capsules or separation of phases or breaking of the capsule wall on spray application which results into failure to achieve the volatility reduction. It was thus desirable to provide a herbicidal formulation having an improved plasticity of the polymeric shell wall to reach an acceptable release rate of the active ingredient clomazone. It is believed that an improvement in plasticity of the polymeric shell wall would substantially reduce the permeation of the shell wall to the active ingredient and possibly limit the breakage of the capsule wall on spray application, which would consequently achieve a substantial reduction in volatility of the formulation.
Another challenge during the encapsulation of clomazone had been its relatively higher water solubility. The known encapsulation methods involve a reaction between an aqueous phase and an organic phase. It was found that the low/mild solubility of clomazone in water did result into poorly defined droplets and also increased the amount of the free active ingredient in the aqueous phase. An increased amount of clomazone in the aqueous phase could contribute to an increased initial “burst effect” administration of clomazone thereby aggravating the risk of plant phytotoxicity and off-target injury due to the volatility of the free clomazone.
U.S. Pat. No. 5,583,090 is directed to a sprayable herbicidal formulation comprising an aqueous liquid having suspended therein a multitude of solid microcapsules having a capsule wall of a porous polymer encapsulating clomazone dissolved in a high boiling inert organic solvent.
U.S. Pat. No. 5,597,780 teaches a process for preparing herbicidally effective formulations of clomazone by microencapsulating clomazone by interfacial polymerization reaction between an aqueous phase and an organic phase. The organic phase essentially comprises a hydrocarbon solvent.
These patents disclose that when the formulations taught therein are sprayed onto one plot containing vegetation, vapor transfer of the herbicide to a nearby plot containing vegetation is effectively suppressed without substantial sacrifice of herbicidal efficacy of the herbicide in the plot to which the spray is applied. However, the problem of reducing the permeability of the polymeric shell wall to the active ingredient consequently limiting the rupture of the capsule wall on spray application and substantially reducing the volatility of the microencapsulated formulation of clomazone still remains a problem. Further, this problem continues to remain irrespective of the chemical nature of the polymeric shell wall such as a polyamide, polyurea, polyurethane, polycarbonate, melamine resin, melamine urea resin, gelatine/gum arabic or cross linked or non-crosslinked combinations thereof.
There is a further need in the art for a microencapsulated formulation of clomazone that is storage stable and capable of being diluted at the time of application as per requirements. These and other needs of the art are met by a microencapsulated formulation of clomazone described hereinafter.